FIG. 1 shows the configuration of a transmission/reception apparatus of a wireless LAN (Local Area Network) which is an example of a radio communication system using OFDM (Orthogonal Frequency Division Multiplexing) which is currently being implemented, and the frame configuration thereof.
FIG. 1(a) shows an example of the configuration of a transmission apparatus and frame configuration signal generation section 10 receives control information 9 such as a modulation scheme as input, determines a frame configuration and outputs frame configuration signal 11. Serial/parallel conversion section (S/P) 2 receives frame configuration signal 11 and baseband signal 1 subjected to digital modulation as input, applies a serial/parallel conversion and outputs parallel signal 3 in accordance with the frame configuration. Inverse Fourier transform (ifft) section 4 receives parallel signal 3 as input, applies Inverse Fourier transform and outputs signal 5 after the Inverse Fourier transform. Radio section 6 receives signal 5 after the Inverse Fourier transform as input, applies a frequency conversion or the like and outputs transmission signal 7. Transmission signal 7 is transmitted as a radio wave from antenna 8.
FIG. 1(b) shows a configuration example of a reception apparatus and radio section 14 receives received signal 13 received at antenna 12 as input, applies processing such as a frequency conversion and outputs baseband signal 15. Synchronization section 16 receives baseband signal 15 as input, establishes time synchronization with a transmitter and outputs timing signal 17. Fourier transform (fft) section 18 receives baseband signal 15 and timing signal 17 as input, applies a Fourier transform to baseband signal 15 based on timing signal 17 and outputs signal 19 after the Fourier transform.
Transmission path fluctuation estimation section 20 receives signal 19 after the Fourier transform and timing signal 17 as input, detects a preamble in the signal after the Fourier transform, estimates a transmission path fluctuation and outputs transmission path fluctuation estimation signal 21. Frequency offset estimation section 22 receives signal 19 after the Fourier transform and timing signal 17 as input, detects preambles and pilot symbols in the signal after the Fourier transform, estimates frequency offset based on these symbols and outputs frequency offset estimation signal 23.
Demodulation section 24 receives signal 19 after the Fourier transform, timing signal 17, transmission path fluctuation estimation signal 21 and frequency offset estimation signal 23 as input, compensates for the transmission path fluctuation and frequency offset in signal 19 after the Fourier transform, demodulates signal 19 and outputs received digital signal 25.
FIG. 1(c) shows an image in a frame configuration of IEEE802.11a (not an exact frame configuration). The vertical axis shows frequency and the horizontal axis shows time, and preambles are inserted at the head to estimate (detect a signal in some cases) a transmission path fluctuation and frequency offset. Furthermore, pilot symbols are inserted in specific carriers such as carrier 2 and carrier 5 and used for the receiver to estimate frequency offset and/or phase noise. The preambles and pilot symbols are those whose signal point constellations on the in-phase I-quadrature Q plane are known. On the other hand, data is transmitted by means of data symbols.
The wireless LAN scheme is described in Non-Patent Document 1.
Non-Patent Document 1: “High speed physical layer (PHY) in 5 GHz band” IEEE802.11a, 1999